DeveloperPrime
DeveloperPrime

Reputation: 111

Boost:condition_variable.notify_one() causes segmentation fault 11 exception

I'm trying to run an example of websocket++ that consists in receive messages from websocket clients and broadcast to all connected clients, but i having problems with thread synchronization.

In the code example the method process_messages waits for message on a std:queue

        boost::unique_lock<boost::mutex> lock(m_action_lock);

        while(m_actions.empty()) {
            m_action_cond.wait(lock);
        }

And the on_message handler locks the queue before to push a new message received from client, but when it try to notify_one(), the program fail with an Segmentation fault 11.

    void on_message(connection_hdl hdl, server::message_ptr msg) {
    // queue message up for sending by processing thread
    {
        boost::unique_lock<boost::mutex> lock(m_action_lock);
        m_actions.push(action(MESSAGE,msg));
        lock.unlock();
    }
    m_action_cond.notify_one();
}

The only way that the program works is commenting the wait(lock) but i not sure if this is safe.

Some body could help me to find de segmentation fault cause?

The complete code is:

#include <websocketpp/config/asio_no_tls.hpp>

#include <websocketpp/server.hpp>

#include <iostream>

#include <boost/thread.hpp>
#include <boost/thread/mutex.hpp>
#include <boost/thread/condition_variable.hpp>

typedef websocketpp::server<websocketpp::config::asio> server;

 using websocketpp::connection_hdl;
 using websocketpp::lib::placeholders::_1;
 using websocketpp::lib::placeholders::_2;
 using websocketpp::lib::bind;

/* on_open insert connection_hdl into channel
 * on_close remove connection_hdl from channel
 * on_message queue send to all channels
 */

enum action_type {
  SUBSCRIBE,
  UNSUBSCRIBE,
  MESSAGE
};

struct action {
  action(action_type t, connection_hdl h) : type(t), hdl(h) {}
  action(action_type t, server::message_ptr m) : type(t), msg(m) {}

  action_type type;
  websocketpp::connection_hdl hdl;
  server::message_ptr msg;
};

class broadcast_server {
public:
  broadcast_server() {
    // Initialize Asio Transport
    m_server.init_asio();

    // Register handler callbacks
    m_server.set_open_handler(bind(&broadcast_server::on_open,this,::_1));
    m_server.set_close_handler(bind(&broadcast_server::on_close,this,::_1));
    m_server.set_message_handler(bind(&broadcast_server::on_message,this,::_1,::_2));
}

void run(uint16_t port) {
    // listen on specified port
    m_server.listen(port);

    // Start the server accept loop
    m_server.start_accept();

    // Start the ASIO io_service run loop
    try {
        m_server.run();
    } catch (const std::exception & e) {
        std::cout << e.what() << std::endl;
    } catch (websocketpp::lib::error_code e) {
        std::cout << e.message() << std::endl;
    } catch (...) {
        std::cout << "other exception" << std::endl;
    }
}

void on_open(connection_hdl hdl) {
    boost::unique_lock<boost::mutex> lock(m_action_lock);
    //std::cout << "on_open" << std::endl;
    m_actions.push(action(SUBSCRIBE,hdl));
    lock.unlock();
    m_action_cond.notify_one();
}

void on_close(connection_hdl hdl) {
    boost::unique_lock<boost::mutex> lock(m_action_lock);
    //std::cout << "on_close" << std::endl;
    m_actions.push(action(UNSUBSCRIBE,hdl));
    lock.unlock();
    m_action_cond.notify_one();
}

void on_message(connection_hdl hdl, server::message_ptr msg) {
    // queue message up for sending by processing thread
    boost::unique_lock<boost::mutex> lock(m_action_lock);
    //std::cout << "on_message" << std::endl;
    m_actions.push(action(MESSAGE,msg));
    lock.unlock();
    m_action_cond.notify_one();
}

void process_messages() {
    while(1) {
        boost::unique_lock<boost::mutex> lock(m_action_lock);

        while(m_actions.empty()) {
            m_action_cond.wait(lock);
        }

        action a = m_actions.front();
        m_actions.pop();

        lock.unlock();

        if (a.type == SUBSCRIBE) {
            boost::unique_lock<boost::mutex> lock(m_connection_lock);
            m_connections.insert(a.hdl);
        } else if (a.type == UNSUBSCRIBE) {
            boost::unique_lock<boost::mutex> lock(m_connection_lock);
            m_connections.erase(a.hdl);
        } else if (a.type == MESSAGE) {
            boost::unique_lock<boost::mutex> lock(m_connection_lock);

            con_list::iterator it;
            for (it = m_connections.begin(); it != m_connections.end(); ++it) {
                m_server.send(*it,a.msg);
            }
        } else {
            // undefined.
        }
      }
  }
 private:
    typedef std::set<connection_hdl,std::owner_less<connection_hdl>> con_list;

    server m_server;
    con_list m_connections;
    std::queue<action> m_actions;

    boost::mutex m_action_lock;
    boost::mutex m_connection_lock;
    boost::condition_variable m_action_cond;
  };

 int main() {
broadcast_server server;

// Start a thread to run the processing loop
boost::thread(bind(&broadcast_server::process_messages,&server));

// Run the asio loop with the main thread
server.run(9002);
 }

Upvotes: 3

Views: 1010

Answers (1)

zaphoyd
zaphoyd

Reputation: 2760

I can reproduce this behavior when Boost is compiled using g++ and libstdc++ but the program linking to it is compiled using clang and libc++. The libstdc++ and libc++ standard libraries are not ABI compatible, so you will need to build everything with one or everything with the other.

Details on how to compile Boost in C++11 mode with clang/libc++:

How to compile/link Boost with clang++/libc++?

Upvotes: 3

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